This invention relates in general to sensing devices and, more particularly, to a sensor for monitoring angular velocity.
Many automotive vehicles of current manufacture come equipped with antilock braking systems and some with traction control systems as well. In a vehicle so equipped, the systems monitor the rotation of some, if not all, of the wheelsxe2x80x94and certainly the front wheels which steer the vehicle. Should a wheel begin to slip when the brakes are applied, as could well occur if the wheel encounters snow or ice, the antilock braking system will detect the loss of velocity and relax the braking force on that wheel. This allows the wheel to continue to rotate and enables the driver to maintain better control over the vehicle. On the other hand, if one of the driving wheels encounters slippery pavement and as a consequence loses traction, the traction control system will apply a braking force to that wheel, and this has the effect of transferring the torque to the opposite wheel which perhaps has better traction.
An antilock braking system or a traction control system for a vehicle thus requires speed sensors to monitor the rotation of some, if not all, of the wheels on the vehicle, and while a variety of locations exist on a vehicle for installation of a speed sensor for a wheel, perhaps the best is in the housing that contains the bearing on which the wheelxe2x80x94or more accurately, the hub for the wheelxe2x80x94rotates. This keeps much of the sensor isolated from contaminants and objects that might otherwise damage it or disrupt its operation. In this regard, the typical sensor of this type fits into a cylindrical hole in the housing and has a stationary probe which is presented toward a target wheel that rotates with the road wheel and contains discontinuities, such as teeth, which the sensor detects as the target wheel revolves. The result is a pulsating signal which reflects the angular velocity of the wheel. A control system monitors the signals from the wheels and initiates braking to achieve the results desired. The spacing between a probe and its target wheel has a significant affect on the operation of the sensor, and it should not vary significantly from the optimum. But many sensors of current manufacture that are installed in housing holes leave much to be desired in this regard.
More specifically, the diameter of the through hole that receives the typical sensor exceeds the diameter of the sensor by a good measure, an as a consequence the sensor is not confined to a fixed radial position in the hole. To be sure, the sensor is fitted with an elastomeric O-ring, which establishes a seal between the sensor and the wall of the hole and further serves to center the sensor in the hole. But as a centering device the O-ring provides little precision and further will enable the sensor to drift laterally from the position it initially assumes. With many activexe2x80x94as opposed to passivexe2x80x94sensor, the target wheel revolves opposite a laterally presented face on the probe of the sensor, and the size of the gap between the side face of the probe and the target wheel is critical. It should remain constant and at an optimum setting.
Aside from that, when a sensor is inserted off center into its hole, a very real danger exists that the O-ring will be damaged during the insertion. This may compromise the fluid barrier that the O-ring normally provides and further can displace the sensor from the center of the hole.
A sensor for installation in a hole in a housing to monitor the rotation of a target wheel in the housing has a bushing and a probe extended from the bushing into the housing where it has a pickup area. An annular elastomeric element encircles the bushing to position the bushing in the hole and a leading surface on the bushing leads up to the elastomeric element to center the bushing in a hole into which it is fitted. The invention also resides in the sensor installed in the housing where the pickup area on its probe is presented toward the target wheel. The housing may contain a bearing, in which event the target wheel rotates with a hub spindle that extends into the housing.